Inter-annual variation in the diet, provisioning and growth of Cassin's auklet at Triangle Island, British Columbia: responses to variation in ocean climate

Abstract

We studied parental provisioning and chick growth rates of Cassin's auklet Ptychoramphus aleuticus at Triangle Island, British Columbia, Canada, from 1996 to 1999. Auklet reproductive performance and ocean climate conditions during these years were highly variable, and reflected in the diet composition. Chick growth was maximal when the diet was predominated by copepods, in particular Neocalanus cristatus. Provisioning and growth were high in 1999, intermediate in 1997 and poor in 1998. Exceptional was 1996, when growth was low but provisioning rates were high. Provisioning and growth were depressed late in 1997 and throughout 1998 when larval rockfish Sebastes spp. (5200 cal g ) in the nestling diet. Zooplankton surveys indicated that N. cristatus was substantially more abundant in May 1999 than in May 1998, and during 1999 the auklets foraged in areas with the highest concentrations of copepods. Through impacts on prey availability, variation in ocean climate affects the reproductive performance of Cassin's auklet. Performance tends to be favorable in years when spring is late and cold, and poor when spring is early and warm. Equations for predicting food delivery rates from 24 h mass changes of chicks were highly year-specific, precluding their application in other years or at other sites where Cassin's auklets breed. Between-year differences were also found in relationships between adult provisioning and chick growth. These were strongly positively related in 1999, positively related in 1996 and 1997, but unrelated in 1998; differences attributed to the magnitude of temporal variation in the nestling diet. Finally, we detected annual differences in parental response to chick needs. In 1999, parents delivered more food to chicks in poor condition and less to those in better condition, responses not observed in 1998. Different responses between years may have reflected variation in the availability of prey.

Differential response in chick survival to diet in least and crested auklets

“…This observation is consistent with other studies, which found that diets high in N. cristatus were associated with high reproductive success in both crested auklets (Fraser et al 2002) and Cassin's auklets (Ptychoramphus aleuticus;Hedd et al 2002). In 2001, the year of lowest chick survival, the hyperiid amphipod Themisto libellula, which has smaller lipid reserves and more refractory chitin than oceanic copepods (Bédard 1969b), was more prevalent in the diet than N. cristatus.…”

“…There is a decline in the transport of Anadyr water past St. Lawrence Island late in the chick-rearing season, reducing the prevalence on high-quality oceanic prey such as Neocalanus copepods (Springer et al 1989). Food availability may, therefore, be the ultimate factor influencing the relationship between early egg laying and high reproductive success (Bertram et al 2001, Hedd et al 2002, Abraham & Sydeman 2004. A change in oceanographic conditions may reduce prey availability beyond the auklet's adaptive response, however, creating a seasonal mismatch between the period of peak copepod availability and chick rearing (Bertram et al 2001, Abraham & Sydeman 2004.…”

“…Alternatively, monitoring nesting seabirds is far less expensive than ship-based monitoring programs and can be used to explore the relationship between avian predators and their marine food supply on a regional scale (Cairns 1987). Reproductive success, diet composition, and adult survival of seabirds may serve as useful indicators of variation in prey availability, as well as changes in large-scale oceanographic conditions , Bertram et al 2000, Hedd et al 2002.…”

Intra-seasonal variation in zooplankton availability, chick diet and breeding performance of a high Arctic planktivorous seabird

“…However, worse quality and quantity of food delivered to chicks of late breeders late in the season may have affected their date of fledging. We have no data to verify it but slower chick growth rate in suboptimal food condition has been documented in the zooplanktivorous Cassin's auklet (Bertram et al 2001, Hedd et al 2002 as well in the little auk in the studied colonies in previous seasons (chicks from Hornsund fledged earlier than in Magdalenefjorden; Jakubas et al 2013).…”

Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey

“…Coincident with the strong La Nina event in 1999, zooplankton biomass increased and the community composition changed within coastal regions of British Columbia , Mackas & Galbraith 2002, Zamon & Welch 2005. In 1999, the reproductive performance of both planktivorous (Cassin's auklet) and piscivorous seabirds (rhinoceros auklet Cerorhinca monocerata and tufted puffin Fratercula cirrhata) on Triangle Island, the largest seabird colony in western Canada, improved dramatically compared to previous years in the 1990s (Bertram et al 2001;Hedd et al 2002;Gjerdrum et al 2003). The trend toward improved breeding performance for these species continued through 2001.…”